A simple nervous system

includes sensory information, an integrating center, and effectors.

Most of the neurons in the human brain are

interneurons

The nucleus and most of the organelles in a neuron are located in the

cell body

The point of connection between two communicating neurons is called the

synapse

In a simple synapse, neurotransmitter chemicals are released by

the presynaptic membrane

Although the membrane of a "resting" neuron is highly
permeable to potassium ions, its membrane potential does not exactly
match the equilibrium potential for potassium because the neuronal me

slighty permeable to sodium ions

The operation of the sodium-potassium "pump" moves

sodium ions out of the cell and potassium ions into the cell

A cation that is more abundant as a solute in the cytosol of a neuron
than it is in the interstitial fluid outside the neuron is

K+

The membrane potential that exactly offsets an ion's concentration
gradient is called the

equilibrium postsynaptic potential

ATP hydrolysis directly powers the movement of

Na+ out of cells

Two fundamental concepts about the ion channels of a
"resting" neuron are that the channels

open and close depending on stimuli, and are specific as to which ion
can traverse them.

Opening all of the sodium channels, with all other ion channels
closed�which is an admittedly artificial setting�on an otherwise
typical neuron should move its membrane potential to

+62 mV

The "selectivity" of a particular ion channel refers to its

permitting passage only to a specific ion.

For a neuron with an initial membrane potential at -70 mV, an
increase in the movement of potassium ions out of that neuron's
cytoplasm would result in the

hyperpolarization of the neuron.

A graded hyperpolarization of a membrane can be induced by

increasing its membrane's permeability to K+.

Self-propagation and refractory periods are typical of

action potentials

The "threshold" potential of a membrane is the

minimum depolarization needed to operate the voltage-gated sodium and
potassium channels

Action potentials move along axons

more rapidly in myelinated than in nonmyelinated axons

A toxin that binds specifically to voltage-gated sodium channels in
axons would be expected to

prevent the depolarization phase of the action potential

After the depolarization phase of an action potential, the resting
potential is restored by

the opening of voltage-gated potassium channels and the closing of
sodium channels.

The "undershoot" phase of after-hyperpolarization is due to

sustained opening of voltage-gated potassium channels

Immediately after an action potential passes along an axon, it is not
possible to generate a second action potential; thus, we state that
the membrane is briefly

refractory

The fastest possible conduction velocity of action potentials is
observed in

thick, myelinated neurons

In the sequence of permeability changes for a complete action
potential, the first of these events that occurs is the

opening of voltage-gated sodium channels

Saltatory conduction is a term applied to

jumping from one node of Ranvier to the next in a myelinated neuron

Two fundamental principles that characterize gated ion channels in
the neuronal membrane are that the channels

open and close depending on stimuli and are specific as to which ion
can traverse them.